Phonon thermal conductance across GaN-AlN interfaces from first principles

Abstract

The vibrational thermal conductances ($G$) across GaN-AlN interfaces are computed using a nonequilibrium Green's function formalism in the harmonic limit with bulk and interfacial interatomic force constants (IFCs) fully from density functional theory. Several numerical methods and supercell configurations are employed to examine the sensitivity of $G$ to variances of IFCs. In particular, the effects of supercell size, the enforcement of symmetry constraints, and truncation of IFCs near the interface, and atomic relaxation on phonon transmission and conductance are explored. Our fully first-principles calculations are compared with common approximations and measured $G$ values inferred from thermal conductivity measurements for GaN-AlN superlattices. Our calculated value, $G\ensuremath{\sim}300\phantom{\rule{0.16em}{0ex}}\mathrm{MW}\phantom{\rule{0.28em}{0ex}}{\mathrm{m}}^{\ensuremath{-}2}\phantom{\rule{0.28em}{0ex}}{\mathrm{K}}^{\ensuremath{-}1}$, is nearly half that from measurements. This discrepancy is critically analyzed in terms of the physical assumptions of the calculations and the derivation of the experimental values. This work provides guidelines to determine ``physically correct'' sets of interfacial IFCs from first principles for thermal conductance calculations using minimal computational resources. It also contributes toward developing predictive calculations and a more complete picture of thermal conduction across interfaces, a step toward first-principles multiscale thermal transport.